While Russia is being heavily criticized by the West for its incursion into Ukraine, the Russian constitution does, in part, allow for this kind of action in a sovereign country.
Article 61, section 2 of the constitution allows defiance of international laws in this situation. It reads, in English:
"The Russian Federation shall guarantee its citizens defense and patronage beyond its boundaries."
This is the language the Russians evoked during the 2008 war with Georgia. And it's language that Russian Foreign Minister Sergey Lavrov referenced Monday, saying, "We are talking here about protection of our citizens and compatriots, about protection of the most fundamental of the human rights—the right to live, and nothing more."
Russian authorities take the language of Article 61 very seriously and uncompromisingly. In 2008, Valery Zorkin, the chief justice of Russia's constitutional court, penned an op-ed on how Article 61 justified the Georgia invasion. He wrote (translated, via Google Translate, emphasis mine), "The government and the president of Russia had no other way than in the strongest terms to ensure compliance with Article 61 of the Constitution, which in black and white that the Russian Federation shall guarantee its citizens protection and patronage abroad."
But, as the Law Library of Congress explains in a legal analysis of the war, that argument is quickly undermined by this fact, a bit of geopolitical trapeze: "The large population of Russian nationals was created artificially by handing Russian citizenship to residents of Georgian separatist regions," the reports states.
Something similar may now be happening in Ukraine. It has been reported that in the past two weeks, Russia issued 143,000 passports for Ukrainians—although, it's not that these Ukrainians are being forced into being geopolitical pawns. Fifty-eight percent of people in the Crimean Peninsula (a sovereign unit under Ukrainian control and landing zone for the Russian military) identify as ethnic Russians. As this map from the BBC shows, 70 percent of those in Crimea supported Ukraine's now-ousted and Russian-backed Prime Minister Viktor Yanukovych.
The Russian legal argument for war didn't stand up to scrutiny in 2008, and it's unlikely to now, seeing how the G-7 countries, identified as the seven wealthiest industrialized nations in the world, have banded together in opposition. And as the United Nations states in its charter very clearly, "All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state."
Cold War Déjà Vu